Mine would have to be the scene which starts of the level in Halo 3 "The Ark".
Nothing says "badass" more than having the Elite ships engage the Brute ships whilst the humans drop onto the Ark.
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^^ Oh yeah, forgot about that game reach. silly game it was. Had the driest campaign with the least(possibly none existent) character development out of all the halo games.... [Edited on 07.05.2012 12:01 AM PDT]